Next, the relation of the amount of increase in intensity
introduced at a single position in such a series to
the amount of error thereby occasioned in the apprehension
of the adjacent intervals was taken up. Two sets
of experiments were carried out, in each of which five
of the sounds were of equal intensity, while one,
occurring in the midst of the series, was louder;
but in one of the sets this louder sound was occasioned
by a fall of the hammer through a distance of 0.875
inch, while in the other the distance traversed was
2.00 inches. In both cases the extent of fall
in the remaining hammers was uniformly 0.25 inch.
The results are given in the following table:

¹Interval B in these experiments
is of the same duration as all
others but that following the louder
sound; hence, judgments in
the second column are correct.

Again the markedly greater influence of increased
intensity on the interval following than on that preceding
it appears, the percentage of errors being, for B
(both intensities), 21.6 per cent.; for A, 56.6 per
cent. Also, in these latter experiments the direction
of error is more definite in the case of interval
A than in that of interval B.

The influence of changes in intensity on the amount
of error produced is striking. Two intensities
only were used for comparison, but the results of
subsequent work in various other aspects of the general
investigation show that this correlation holds for
all ranges of intensities tested, and that the amount
of underestimation of the interval following a louder
sound introduced into an otherwise uniform series
is a function of the excess of the former over the
latter. The law holds, but not with equal rigor,
of the interval preceding the louder sound. So
far as these records go, the influence of such an
increase of intensity is more marked in the case of
interval B than in that of interval A. It is to be
noted, however, that the absolute percentage of errors